CASE STUDY SNAPSHOT
Customer : A healthcare technology startup based in the United States focused on patient safety and location monitoring solutionsSize : < 50
Project vertical : Healthcare, Consumer Electronics, IoT
Challenge : Design and develop a personal tracker technology demonstrator for monitoring the location and health of autistic patients, combining LoRa for deep indoor penetration, BLE for home zone detection, and GPS for outdoor tracking, with PPG health monitoring, accelerometer activity sensing, OTA update capability, and five days of battery life in a wearable form factor.
Solution : Personal tracker technology demonstrator on NXP KW36A BLE SoC with LoRa for indoor/dense urban tracking, BLE for home zone proximity detection, GPS for outdoor location, SI-based PPG sensor for health monitoring, accelerometer for activity tracking, OTA firmware update over LoRa and USB, and optimised power management for five-day battery life.
Services & Products Availed : Turnkey Product Engineering, Embedded Hardware Design, Embedded Firmware Development
Tools and Technologies :
- Target SoC: NXP KW36A (ARM Cortex-M0+, BLE 5.0)
- Connectivity: LoRa (8-mile range), BLE 5.0, GPS
- Health Sensors: PPG (heart rate, HRV, SpO2), Accelerometer
- OTA: LoRa-based and USB-based firmware update
- Power: LiPo battery, intelligent power management
- Form Factor: Wrist/arm band, ring, eyeglass, shoe wearable
- Languages: C
- Tools: MCUXpresso IDE
Introduction
Autistic individuals, particularly children and adults with limited communication ability or spatial awareness, are at elevated risk of wandering and becoming lost. Caregivers and families of autistic individuals face the constant challenge of maintaining awareness of their loved one's location and safety without imposing restrictive supervision that limits independence and quality of life. A personal tracking device that can reliably locate an individual across the full range of environments they encounter, indoors in a home, school, or care facility, in dense urban areas, and outdoors, while monitoring their health and activity, would give caregivers the situational awareness they need with minimal intrusiveness.
A healthcare technology startup in the United States, focused on patient safety and location monitoring solutions for autistic individuals, approached Embien to develop a personal tracker technology demonstrator. The device had to combine three complementary location technologies, LoRa for deep indoor and dense urban penetration, BLE for home zone proximity detection, and GPS for outdoor location accuracy, into a wearable device that could sustain five days of operation on a single charge, monitor the wearer's heart rate and activity, and support firmware updates in the field over both LoRa and USB.
Challenge
The multi-mode location strategy was the defining technical challenge. Each location technology excels in a specific environment and fails in others, GPS provides accurate outdoor positioning but cannot penetrate building structures; BLE provides reliable short-range proximity detection but has limited range; LoRa provides deep indoor penetration and kilometre-scale range but provides only coarse location through gateway triangulation rather than precise GPS coordinates. Integrating all three technologies into a single device and implementing the context-aware switching logic that selects the appropriate technology based on the wearer's environment required careful firmware architecture and power management design.
The five-day battery life target was extremely demanding for a device that simultaneously manages three radio technologies, LoRa, BLE, and GPS, alongside PPG health monitoring and accelerometer sensing. Each radio represents a significant power draw when active, and naive management of all radios simultaneously would reduce battery life to hours rather than days. The power management strategy had to aggressively duty-cycle each subsystem, keeping radios and sensors in their lowest possible power state for the maximum possible fraction of time, while maintaining the location awareness and health monitoring responsiveness required for the autistic patient safety use case.
The wearable form factor, designed to be worn as a wrist or arm band, ring, eyeglass mount, or shoe insert based on the individual's preference, imposed strict constraints on PCB size, battery capacity, and mechanical design that amplified the power management challenge. The device had to be compact and unobtrusive enough that an autistic individual would accept and tolerate wearing it continuously, a critical adoption requirement for a patient safety device.
Supporting OTA firmware updates over LoRa, the long-range radio, was a technically interesting challenge. LoRa's low data rate means that a firmware image of even modest size requires an extended transfer time, and the transfer protocol had to be designed for reliable, resumable delivery over a radio channel that may experience intermittent packet loss.
Solution
NXP KW36A SoC Platform
The personal tracker is built around the NXP KW36A, a System-on-Chip integrating an ARM Cortex-M0+ microcontroller with a BLE 5.0 radio, designed specifically for automotive-grade and IoT wearable applications. The KW36A's combination of BLE connectivity, sufficient processing capability for the tracker's sensor fusion and location logic, low-power operating modes, and compact package made it the appropriate heart of the personal tracker design. External modules for LoRa and GPS were interfaced to the KW36A over UART and SPI, with the KW36A firmware managing the power state and communication with each external module.
Multi-Mode Location Architecture
The location system implements a three-tier hierarchy of location technologies, selected based on the wearer's detected environment and the availability of each technology's infrastructure.
BLE home zone detection operates continuously at the lowest power level, the KW36A's integrated BLE radio scans periodically for a designated home zone BLE beacon installed at the wearer's home or primary care location. When the home zone beacon is detected, the device reports the wearer as present in the home zone and suppresses LoRa and GPS activity, conserving power and providing the caregiver with the assurance that the individual is within the defined safe area. BLE RSSI is used to detect when the wearer moves beyond the home zone beacon's range, triggering transition to the LoRa tracking mode.
LoRa tracking activates when the wearer is outside the home zone, providing location coverage in indoor environments, dense urban areas, and any location where LoRa gateway infrastructure is available. LoRa operates in the 865MHz band, providing the deep building penetration and kilometre-scale range, up to 8 miles in open terrain, that makes it effective for tracking in environments where GPS signals are unavailable. The tracker transmits periodic location beacons over LoRa, received by LoRa gateways in the infrastructure, with the gateway network computing the tracker's approximate location through signal strength triangulation and reporting it to the cloud backend. This provides coarse but useful location information even in challenging indoor environments.
GPS tracking activates when the device detects that it is in an outdoor environment with clear sky access, identified through successful GPS fix acquisition. GPS provides precise coordinate-level location accuracy for outdoor tracking, with position reports transmitted to the cloud backend over the LoRa uplink. GPS is the most power-intensive location mode and is therefore active only when the device's context detection confirms outdoor conditions where GPS is both available and most useful.
PPG Health Monitoring
PPG-based health monitoring provides the caregiver with visibility into the wearer's physiological state alongside their location. The PPG sensor measures heart rate, heart rate variability, and SpO2, indicators of stress, anxiety, and physical exertion that are clinically relevant in the autistic patient monitoring context. Accelerometer data is used in conjunction with the PPG signal to apply motion artefact rejection, improving the reliability of heart rate readings during movement.
Activity tracking data, step count, calories burned, and distance, is derived from the accelerometer and included in the health data reported to the cloud backend, providing caregivers with a record of the wearer's daily activity pattern.
Heart rate and activity data are sampled at a configurable interval and transmitted to the cloud alongside location updates, giving caregivers an integrated view of the wearer's location and physiological state from the companion monitoring application.
Intelligent Power Management
Five-day battery life was achieved through systematic power management across every subsystem. The KW36A core operates in deep sleep between scheduled wake events, consuming only microamps during sleep. The LoRa module is powered down between transmission intervals, powered on only for the duration of each beacon transmission and the brief receive window that follows. GPS is duty-cycled based on environment context, active only in confirmed outdoor conditions and powered down immediately once a fix is obtained and transmitted. The PPG sensor and its LED emitters are powered on only during scheduled measurement intervals. Peripheral power gating is implemented through dedicated power control lines managed by the firmware's power sequencer, ensuring that no subsystem draws quiescent current during its inactive periods.
BLE advertising interval, LoRa transmission interval, GPS sampling rate, and PPG measurement interval are all configurable through the device's cloud management interface, enabling the caregiver or system operator to trade off between location update frequency and battery life based on the specific monitoring requirements of the individual wearer.
OTA Firmware Update over LoRa and USB
Firmware updates are supported over both LoRa and USB, providing flexibility for field update in any deployment scenario. The LoRa OTA update mechanism implements a reliable, segmented transfer protocol over the LoRa uplink, dividing the firmware image into small packets sized for LoRa's constrained payload, with sequence numbering, acknowledgement, and retransmission handling to ensure reliable delivery despite occasional packet loss. Download progress is checkpointed, enabling a partially completed download to be resumed after interruption rather than restarted. The USB OTA path provides a faster, higher-reliability update channel for situations where the device can be brought to a connected location, using a simple USB bulk transfer protocol to deliver the firmware image at USB data rates. Both paths validate the received image's integrity before programming, protecting against corrupted updates reaching the bootloader.
Benefits
- Three-mode location coverage - BLE home zone detection, LoRa indoor and dense urban tracking, and GPS outdoor positioning provide complementary location coverage across the full range of environments encountered by autistic individuals, with context-aware mode selection minimising power consumption
- 8-mile LoRa range with deep indoor penetration - LoRa's 865MHz propagation characteristics deliver tracking capability in buildings, basements, and dense urban environments where GPS is unavailable, providing location awareness in the indoor environments most relevant to the autistic patient safety use case
- Five-day battery life - Systematic duty-cycling of all radio and sensor subsystems with context-aware activation delivers five days of continuous tracking and health monitoring from a wearable-appropriate battery capacity
- Integrated PPG health monitoring - Heart rate, HRV, SpO2, and activity tracking provide caregivers with physiological context alongside location data, supporting detection of stress, anxiety, and health events in non-verbal autistic individuals
- Dual-path OTA firmware update - LoRa-based segmented OTA with resumable transfer and USB-based high-speed update provide flexible, field-deployable firmware update capability for devices distributed across geographically dispersed care locations
Conclusion
This LoRa and BLE personal tracker technology demonstrator reflects Embien's capability to develop sophisticated multi-mode location and health monitoring wearables for healthcare applications. By combining LoRa, BLE, and GPS location technologies in a context-aware architecture, alongside PPG health monitoring and aggressive multi-subsystem power management, Embien demonstrated a personal tracker concept capable of providing reliable, continuous location and health awareness for autistic individuals across indoor, urban, and outdoor environments within a five-day battery life constraint. This project reflects Embien's experience in multi-radio embedded design, ultra-low power wearable firmware development, and healthcare IoT applications, a combination increasingly relevant as connected health monitoring technology addresses the safety and care challenges faced by individuals with complex needs.